Field
The described technology generally relates to antenna systems and methods for controlling wave polarization, specifically to controlling linear polarization with multiple polarization components.
Description of the Related Art
Ku-band antennas operating with linearly polarized (LP) satellite waves often utilize continuous polarization alignment to maximize sending and receiving the desired LP wave while minimizing the interference from an orthogonal LP wave. Satellite communications for fixed satellite services (FSS) and for vehicular mobile earth stations (VMES) typically use dual-linear orthogonal polarizations on the user link for two-way communications. In typical systems, the linear polarizations include vertical and horizontal polarizations, and the satellite antenna is oriented in the satellite coordinate system in a way that the vertical polarization is aligned true north-south as seen by an earth station located at a sub-satellite point on Earth. The horizontal polarization is aligned in a true east-west orientation at the sub-satellite point. Earth stations receiving these waves also typically utilize linearly polarized antennas having a fixed orientation in a local coordinate system defined by the earth station (mobile or fixed). The orientation of the two orthogonal linear polarizations of the satellite transmission will rotate in the local earth station coordinate system as the earth station moves and changes orientation with respect to true north-south of the Earth. It is therefore necessary to perform polarization tracking as a mobile earth station moves to dynamically match the rotation of the polarization of the satellite signals as seen by the earth station.
It is often the practice in the case of circular reflector antennas to mechanically rotate the entire antenna assembly to match the rotation of the fixed satellite polarizations. Alternatively, the feed subassembly including the polarization mode launch subassembly may be rotated.
In the case of panel type mobile earth station antennas that have a significant aspect ratio (e.g., width/height greater than 3:1), a combining technique may be used. For example, a Ku-band panel type mobile earth station with dual linearly polarized antennas can use a mechanical actuated or electronic control component to combine the two linearly polarized components to produce a rotated set of linearly polarized components to match the satellite polarization. This can be accomplished by a pair of orthomode transducers (OMTs) arranged with a common port axis and mechanically rotating one while holding the other stationary, or by a variable power combiner or divider (VPC or VPD) radio frequency (RF) circuit. The VPC or VPD may use phase shifting and passive 4-port hybrid type circuits to achieve a variable amplitude control.